Sci. Adv. 4, eaas9459 (2018)

Metal nanoporous structures combine good electrical and mass transport with high surface area to volume ratio, which makes them promising for supercapacitors and catalysis applications. Such structures can be obtained by de-alloying binary metallic alloys. For example, nanoporous gold is often created by dissolution of silver from a silver–gold alloy. Despite encouraging results obtained in the past, a limitation of nanoporous gold is that the pore structure is usually fairly random and generates considerable resistance to mass flow.

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AAAS

Now, Cheng Zhu et al. have fabricated hierarchical nanoporous gold by the combination of 3D printing with alloying and de-alloying. Large macroscopic pores, of the order of micrometres or even tens of micrometres, can be used as preferential channels for mass transport, while a finer structure of pores in the tens of nanometres range ensures a high surface to volume ratio. The first step of the fabrication process is the 3D printing of a porous macrostructure of gold and silver microparticles, which is then annealed to form a homogeneous Au–Ag alloy. Eventually, the alloy is immersed in an etching agent that removes the silver, leaving a porous nanostructure with typical features in the 10–100 nm range.

The hierarchical non-porous structure substantially outperforms its non-hierarchical analogue in terms of electrochemical, mass-transport and catalytic properties.